For many years, wire form metal products have been a superior substitute for sheet metal or molded compositions in many applications. Wire form imparts increased strength to the article of manufacture while often reducing its weight substantially. The rounded corners and flexibility of wire form articles have found applications in the medical field as well where wire forms provide the ability to conform to irregular geometries and shapes. Such geometries and shapes can provide, for example, inner rods to hollow bore needles or to facilitate the delivery of stents in the body.
It is often desirable to have a wire with a cross-section other than round. Wires with cross-sections that are rectangular, triangular, square or some other unique geometry may be desirable. To achieve a unique cross-section in the wire, a forming process is utilized, which transforms a round wire into the desired cross-section. The forming process involves a set of rollers, where the round wire is passed between the rollers and the new geometry is pressed into the round wire. The roller set consists of a top 1 and bottom roller 2, as shown in FIG. 1, each of which have a circumferential forming groove, 3 and 4, respectively, formed into it. The groove acts as the mold or forming surface to press the round wire into the desired geometry. As a result, round wire enters the forming system, and formed wire with some other cross-sectional geometry exits the system.
Because some cross-sections may require more than one forming step in order to be transformed from round to the desired cross-section, a series of forming rollers is often utilized. The round wire is incrementally formed from round to the desired cross-section as it passes through each sequential forming station. This is because the amount of material movement that can occur in one stage of forming is limited by the material characteristics of the metal comprising the wire. Progressive forming involves the use of multiple stages which each accomplish incremental forming steps.
Currently, as shown in FIG. 2, the incremental forming process consists of individual roller sets 1, 1a and 1b arranged in a linear series, the wire 2 passing from one set to the next in each stage of the process. The wire is suspended freely between roller sets 1, 1a and 1b requiring the orientation of the wire be the same from one roller set to the next in order to fit properly within the forming grooves. Where the wire is suspended freely between roller sets, the wire spatial orientation is free to change, i.e., rotate or otherwise move out of the alignment orientation necessary to continue forming. Thus, maintaining the correct wire orientation as it passes to progressive sets of rollers can be difficult. A misfeed in the wire between roller stages, wherein the wire adopts the improper orientation and lodges within the grooves, often requires simply restarting the process anew. A more uniform method of ensuring the wire retains its correct orientation for the next forming stage would be desirable.